A Code Division Multiple Access (CDMA) Communication system is designed to operate over a bandwidth of a fixed size. For example, a 1x-EVDO communication system operates on 1.25 MHz bandwidth. Because of this limited resource, resource management plays an important role in a CDMA communication system. In a 1x-EVDO communication system, a base transceiver station (BTS) serves the communication needs of access terminals (ATs) in the coverage area of the BTS. An AT may be a wireless phone, wireless equipped PDA or computer, etc.; and may also be referred to as a mobile station or mobile unit. Communication from the BTS to an AT is referred to as forward or down link communication, and communication from an AT to the BTS is referred to as reverse or uplink communication.
The current version of the 1x-EVDO standard provided in 3GPP2 C.S0024-A v2.0, sets forth a resource management methodology in the reverse link based on a bucket filling concept and is hereby incorporated by reference in its entirety. Because this standard is so well-known, the standard, as it pertains to the subject invention, will not be described in detail; but instead, will only be briefly discussed. Furthermore, this description, for the sake of brevity, will concern reverse link resource management.
In the reverse link of a 1x-EVDO Revision A system, there are a total of 6 channels per user: one traffic channel and five overhead channels. The five overhead channels include a pilot channel, a data rate control (DRC) channel, a data source control (DSC) channel, an acknowledgement (ACK) channel, and a reverse rate indication (RRI) channel. The pilot channel is used for channel estimation of the air interface between the BTS and the AT, and is used for power control purposes. Power control makes sure that the received pilot channel power at the BTS is stable and results in a stable channel estimation. Accordingly, transmission power of the other channels are defined by channel gains with respect to the pilot channel. For the traffic channel, the transmit power is specified by a power gain called the traffic-to-pilot (T2P) power gain.
The bucket filling methodology present in the 1x-EVDO RevA standard treats T2P as a resource, which may be accumulated and used. Typically, a bucket is defined for each radio link flow; for example, data flow from one of the applications running at the AT. For simplicity, the bucket filling methodology will be described for the case of a single radio link or application flow. However, it will be understood that 1x-EVDO provides for managing the T2P resource for multiple link flows.
The amount of T2P resource added to the bucket is referred to as the T2PInflow, and the amount of T2P resource used is referred to as the T2POutflow. As a result, the amount of T2P resource in the bucket, referred to as the BucketLevel, is a function of the T2PInflow and the T2POutflow.
The AT determines the T2PInflow based on reverse activity bits (RABs) received by the AT from the BTS and a pilot signal strength of the forward link pilot signal. The BTS transmits a RAB to an AT per time slot (a short time duration) to inform the AT of the loading condition at the BTS. If the loading, or the total received power, is below a threshold, the RAB bit is set to “0”. Otherwise, if the loading is above a threshold, the RAB bit is set to “1”. The value of the RAB bits indicates the current loading condition at the base station. The RAB bit is binary modulated (e.g., to “−1” for a value of “0” and “1” for a value of “1”) and transmitted to the AT. Using the RABs received over time, the AT determines a quick RAB (QRAB) and a filtered RAB (FRAB). Both the QRAB and FRAB are filtered versions of the RABs received over time, but the QRAB has a significantly smaller time constant than that of the FRAB. In other words, the QRAB is a short term load indicator, and the FRAB is a long term load indicator. The AT determines the T2PInflow as a function of the QRAB, FRAB and measured pilot strength.
Based on the T2P inflow and BucketLevel, the AT determines a potential outflow for transmission, referred to as PotentialT2POutflow. The PotentialT2POutflow indicates the amount of T2P resource that may be used during transmission; and therefore, indicates the amount of available T2P resource for the current transmission. The Potential P2POutflow is a function of the BucketLevel, the FRAB, the T2PInflow, and a BucketFactor. The BucketFactor indicates by what factor the T2POutflow may exceed the T2PInflow. Using the PotentialT2POutflow, the AT determines the packet size for transmission, and the actual power or T2P used in transmission, referred to as TxT2P, is determined as a function of the packet size and the transmission mode. As is known, the AT may operate in a low latency (LoLat) transmission mode or a high capacity (HiCap) transmission mode.
As will be appreciated, the transmitted packet includes headers, etc., according to protocol in addition to the data d from the application. Accordingly, after transmission, the AT determines the T2POutflow as a function of the data d (usually expressed in octets) and the TxT2P.
As will be appreciated, this description merely provides an overview of the resource management methodology in 1x-EVDO, and the exact details for the various functions, etc. mentioned above are well-known and may be readily obtained from the standard. In addition, for the sake of simplicity, this overview has excluded mentioning the various constraints such as minimum and maximum permitted T2PInflow, that one skilled in the art will appreciate are included in the methodology.
While the above described resource management methodology aids in improving capacity and meeting quality of service (QoS) requirements for subscribed ATs, the single carrier architecture discussed above may not meet the needs created by increasing amounts of data traffic. As a result, more and more bandwidth is demanded in order to support a greater number of users and higher data throughout. Without introducing too much change to the core of the single-carrier design in 1x-EVDO, a Multiple-Carrier CDMA (MC-CDMA) system has been suggested to scale the system capacity when more bandwidth is available. For instance, if 5 MHz of bandwidth is available, then a 3-carrier 1x-EVDO system may be used to increase the capacity of a single-carrier 1x-EVDO system by at least 3 times. In its simplest form, each carrier is managed independently according to the 1x-EVDO standard.
The operation of MC-CDMA systems presents several challenges and provides several opportunities in the areas of resource management. For example, an MC-CDMA system should maintain the QoS (Quality of Service) for different applications while minimizing the resources consumed. Secondly, the MC-CDMA should be able to exploit multiple carrier diversity gain. Thirdly, the MC-CDMA system should be able to achieve load balancing among carriers, and exploit pooling efficiency within the system.